Question: Which of these numbers is composite? ${3,\ 5,\ 19,\ 71,\ 85}$
A composite number is a number that has more than two factors (including 1 and itself). 3, 5, 19, and 71 each have only two factors. The factors of 85 are 1, 5, 17, and 85. Thus, 85 is the composite number.